The present invention relates to a heat exchanger, in particular a charge air cooler for a motor vehicle.
In order to achieve an increase in the power of an internal combustion engine, the air to be supplied for combustion can be compressed, for example, by means of a turbocharger before it is supplied to the combustion chambers of the internal combustion engine. At the same time, however, the compression of the air entails a heating of the latter which is a disadvantage for an optimum flow of the combustion process. For example, premature ignition or increased nitrogen oxide emission may be triggered as a result. In order to avoid the adverse consequences of overheated air supplied for combustion, a turbocharger is followed by a heat exchanger which is designed as a charge air cooler and by means of which the compressed air can be cooled to a permissible temperature before its combustion.
A charge air cooler is described, for example, in DE 197 57 034 A1. In the heat exchanger there, the hot air is introduced into a first collecting duct of the heat exchanger, where it is distributed and flows into flat tubes which issue into the collecting duct. The flat tubes are arranged next to one another, and with the side faces containing the long sides of their cross section being parallel to one another, and form a flow path by means of which cooling air is conducted through. The flow path has arranged in it, between the flat tubes, cooling ribs which bring about an effective heat exchange between the flat tubes and the cooling air stream. After crossing the cooling air stream, the flat tubes issue in a second collecting duct which supplies the cooled compressed charge air flowing into the latter for combustion in the engine.
In heat exchangers, such as, in particular, charge air coolers of this type, the tubes are conventionally inserted in orifices of a tube plate and soldered in a fluidtight manner. Whenever there is a charge of compressed air, this soldered joint undergoes high mechanical loads due to rapid pressure changes. Especially the narrow sides of flat tubes do not meet the mounting strength requirements, and therefore leaks may occur particularly at the corners of such tube plate connections.
A simpler way of increasing the strength of tube plate connections is to use tubes with a greater wall thickness or outer and/or inner ribs of greater material thickness. The increased mechanical stability is clear in both instances, but the extra outlay required for this purpose in terms of material costs and material weight is very high.
Other solution proposals are concerned with reducing the mechanical stress on the tube plate connections, for example by the use of tie rods in the charge air boxes. These tie rods stabilize the charge air boxes and thereby relieve the tube plate connections, but entail an increase in the pressure loss caused by the charge air cooler.